In this photo taken Friday, Nov. 23, 2012, Neal Kingston, director of the Center for Educational Testing and Evaluation at the University of Kansas, talks about testing fraud in his Lawrence, Kan., office. Theres a never-ending war between those who try to maintain standards and those who are looking out for their own interests," says Kingston. (AP Photo/Charlie Riedel) | AP

MEMPHIS, Tenn. -- It was a brazen and surprisingly long-lived scheme, authorities said, to help aspiring public school teachers cheat on the tests they must pass to prove they are qualified to lead their classrooms.

For 15 years, teachers in three Southern states paid Clarence Mumford Sr. – himself a longtime educator – to send someone else to take the tests in their place, authorities said. Each time, Mumford received a fee of between $1,500 and $3,000 to send one of his test ringers with fake identification to the Praxis exam. In return, his customers got a passing grade and began their careers as cheaters, according to federal prosecutors in Memphis.

Authorities say the scheme affected hundreds – if not thousands – of public school students who ended up being taught by unqualified instructors.

Mumford faces more than 60 fraud and conspiracy charges that claim he created fake driver's licenses with the information of a teacher or an aspiring teacher and attached the photograph of a test-taker. Prospective teachers are accused of giving Mumford their Social Security numbers for him to make the fake identities.

The hired-test takers went to testing centers, showed the proctor the fake license, and passed the certification exam, prosecutors say. Then, the aspiring teacher used the test score to secure a job with a public school district, the indictment alleges. Fourteen people have been charged with mail and Social Security fraud, and four people have pleaded guilty to charges associated with the scheme.

Mumford "obtained tens of thousands of dollars" during the alleged conspiracy, which prosecutors say lasted from 1995 to 2010 in Arkansas, Mississippi and Tennessee.

Among those charged is former University of Tennessee and NFL wide receiver Cedrick Wilson, who is accused of employing a test-taker for a Praxis physical education exam. He was charged in late October with four counts of Social Security and mail fraud. He has pleaded not guilty and is out of jail on a $10,000 bond. He has been suspended by the Memphis City Schools system.

If convicted, Mumford could face between two and 20 years in prison on each count. The teachers face between two and 20 years in prison on each count if convicted.

Lawyers for Mumford and Wilson did not return calls for comment.

Prosecutors and standardized test experts say students were hurt the most by the scheme because they were being taught by unqualified teachers. It also sheds some light on the nature of cheating and the lengths people go to in order to get ahead.

"As technology keeps advancing, there are more and more ways to cheat on tests of this kind," said Neal Kingston, director of the Center for Educational Testing and Evaluation at the University of Kansas. "There's a never-ending war between those who try to maintain standards and those who are looking out for their own interests."

Cheating on standardized tests is not new, and it can be as simple as looking at the other person's test sheet. The Internet and cell phones have made it easier for students to cheat in a variety of ways. In the past few years, investigations into cheating on standardized tests for K-12 students have surfaced in Atlanta, New York and El Paso, Texas.

Still, most of the recent test-taking scandals involved students taking tests, not people taking teacher certification exams. Cheating scams involving teacher certification tests are more unusual, said Robert Schaeffer, public education director for the National Center for Fair & Open Testing.

Schaeffer notes that a large-scale scandal involving teacher certification tests was discovered in 2000, also in the South. In that case, 52 teachers were charged with paying up to $1,000 apiece to a former Educational Testing Services proctor to ensure a passing grade on teacher certification tests.

Teachers from Arkansas, Georgia, Louisiana, Tennessee and Mississippi took tests through Philander Smith College in Little Rock, Ark., in 1998. The college was not accused of wrongdoing.

Educational Testing Services also writes and administers the Praxis examinations involved in the Memphis case. ETS spokesman Tom Ewing said the company discovered the cheating in June 2009, conducted an investigation and canceled scores. The company began meeting with authorities to turn over the information in late 2009, Ewing said.

"These cases are rare, but we consider them to be very serious and something we have to guard against happening for all the honest test-takers, students and teachers," Ewing said.

Ewing said ETS observes test-takers and reviews test scores to try to root out cheaters. ETS also has received anonymous tips that have led them to cheaters, Ewing said.

Prosecutors in the Mumford case say he, the teachers and test-takers used the Internet and the U.S. Postal Service to register and pay for the tests, and to receive payment. The indictment does not say how much he allegedly paid the test-takers.

An experienced educator, Mumford was working for Memphis City Schools when the alleged scam took place. Authorities say Mumford defrauded the three states by making the fake driver's licenses.

"What happens at many testing centers is that a whole bunch of test-takers show up simultaneously, early on a Saturday morning, and the proctors give only a cursory look to the identification," Schaeffer said. "It's not like going through airport security where a guy holds up a magnifying glass and puts our license under ultraviolet light to make sure it has not been tampered with."

Mumford was fired after news of the investigation came out, and others, like Wilson, have been suspended. But at least three teachers implicated in the scandal remain employed with their school district.

Kingston, the university professor, said prospective teachers may not be confident in their knowledge base to pass the test. Or, the cheaters may believe they are smart enough to pass on their own but also know they are poor test takers.

Kingston said his research has shown that cheating on exams is getting more prevalent.

"The propensity to cheat on exams both through college and for licensure and certification exams seems to be increasing over time," said Kingston. "People often don't see it as something wrong."

The pressure of passing the test could make people do things they normally would not do. And it could take a while for authorities and test-taking services to catch up with the cheaters.

"When people come up with a new method for cheating, it takes some time for folks to figure it out, partly because this has been an understudied area in the field of assessment," Kingston said.

Nina Monfredo, a 23-year-old history teacher at Power Center Academy in Memphis, has taken Praxis exams for history, geography, middle school content, and secondary teaching and learning.

Monfredo, who passed all her tests and is not involved in the fraud case, said the exams she took were relatively easy for someone who has a high school education. She said some people use study aids to prepare, but she didn't. And she didn't feel much pressure because it was her understanding that she could take the test again if she did not pass.

"If you feel like you can't pass and you hire someone it means you really didn't know what you were doing," she said. "I think it would be easier to just learn what's on the test."